Buggy code:
public final class IdStrategy implements GraphStrategy { private final String idKey ; private final Supplier < ? > edgeIdSupplier ; private final Supplier < ? > vertexIdSupplier ; private final boolean supportsVertexId ; private final boolean supportsEdgeId ; private IdStrategy ( final String idKey , final Supplier < ? > vertexIdSupplier , final Supplier < ? > edgeIdSupplier , final boolean supportsVertexId , final boolean supportsEdgeId ) { } @ Override public UnaryOperator < Function < Object [ ] , Vertex > > getAddVertexStrategy ( final StrategyContext < StrategyGraph > ctx , final GraphStrategy composingStrategy ) { } @ Override public UnaryOperator < TriFunction < String , Vertex , Object [ ] , Edge > > getAddEdgeStrategy ( final StrategyContext < StrategyVertex > ctx , final GraphStrategy composingStrategy ) { } @ Override public UnaryOperator < Function < Object [ ] , Iterator < Edge > > > getGraphIteratorsEdgeIteratorStrategy ( final StrategyContext < StrategyGraph > ctx , final GraphStrategy composingStrategy ) { <START_BUG> return supportsVertexId ? ( f ) -> ( ids ) -> ctx . getStrategyGraph ( ) . getBaseGraph ( ) . traversal ( ) . E ( ) . has ( idKey , within , Arrays . asList ( ids ) ) : UnaryOperator . identity ( ) ; <END_BUG> } @ Override public UnaryOperator < Function < Object [ ] , Iterator < Vertex > > > getGraphIteratorsVertexIteratorStrategy ( final StrategyContext < StrategyGraph > ctx , final GraphStrategy composingStrategy ) { } @ Override public UnaryOperator < Function < Object [ ] , GraphTraversal < Edge , Edge > > > getGraphEStrategy ( final StrategyContext < StrategyGraph > ctx , final GraphStrategy composingStrategy ) { } @ Override public UnaryOperator < Function < Object [ ] , GraphTraversal < Vertex , Vertex > > > getGraphVStrategy ( final StrategyContext < StrategyGraph > ctx , final GraphStrategy composingStrategy ) { } @ Override public UnaryOperator < Supplier < Object > > getVertexIdStrategy ( final StrategyContext < StrategyVertex > ctx , final GraphStrategy composingStrategy ) { } @ Override public UnaryOperator < Supplier < Object > > getEdgeIdStrategy ( final StrategyContext < StrategyEdge > ctx , final GraphStrategy composingStrategy ) { } @ Override public < V > UnaryOperator < BiFunction < String , V , VertexProperty < V > > > getVertexPropertyStrategy ( final StrategyContext < StrategyVertex > ctx , final GraphStrategy composingStrategy ) { } @ Override public < V > UnaryOperator < BiFunction < String , V , Property < V > > > getEdgePropertyStrategy ( final StrategyContext < StrategyEdge > ctx , final GraphStrategy composingStrategy ) { } @ Override public String toString ( ) { } private void throwIfIdKeyIsSet ( final Class < ? extends Element > element , final String k ) { } private void throwIfIdKeyIsSet ( final Class < ? extends Element > element , final Set < String > keys ) { } private boolean supportsAnId ( final Class < ? extends Element > element ) { } public String getIdKey ( ) { } public boolean isSupportsVertexId ( ) { } public boolean isSupportsEdgeId ( ) { } private List < Object > injectId ( final boolean supports , final Object [ ] keyValues , final Supplier < ? > idMaker ) { } public static IdStrategy . Builder build ( final String idKey ) { } public static final class Builder { private final String idKey ; private Supplier < ? > vertexIdSupplier ; private Supplier < ? > edgeIdSupplier ; private boolean supportsVertexId ; private boolean supportsEdgeId ; private Builder ( final String idKey ) { } public IdStrategy create ( ) { } public IdStrategy . Builder vertexIdMaker ( final Supplier < ? > vertexIdSupplier ) { } public IdStrategy . Builder edgeIdMaker ( final Supplier < ? > edgeIdSupplier ) { } public IdStrategy . Builder supportsEdgeId ( final boolean supports ) { } public IdStrategy . Builder supportsVertexId ( final boolean supports ) { } private static String supplyStringId ( ) { } } }

Fix:
return supportsEdgeId ? ( f ) -> ( ids ) -> ctx . getStrategyGraph ( ) . getBaseGraph ( ) . traversal ( ) . E ( ) . has ( idKey , within , Arrays . asList ( ids ) ) : UnaryOperator . identity ( ) ;